This invention relates to a method and apparatus for testing the resistance between the windings of an electric motor and a terminal connector. Specifically, this invention relates to a motor armature tester for measuring the resistance of individual windings and the contact resistance between a commutator bar and the windings connected thereto.
In testing motor armatures, especially on high speed production lines, the resistance of the windings themselves is measured, and then the resistance of the connection between the windings and the commutator is determined. In a typical appliance motor, the resistance measured across a pair of commutator bars is in the order of 200 mOhm whereas the maximum permissible contact resistance between the windings and the commutator is about 0.1% of that amount, or about 0.2 mOhm. Since the tolerance on the winding resistance is approximately .+-.5%, or from .+-.10 mOhm in this example, this tolerance clearly is far greater than the expected variation in connection resistance, thus requiring careful and accurate measurement techniques to be used.